Fuel cell electric vehicles have become the object of increasing attention in recent years from the viewpoint of environmental concerns, such as reducing carbon dioxide emissions that are a cause of global warming. Fuel cell electric vehicles are furnished with fuel cells that generate electrical power by electrochemical reaction of hydrogen with oxygen in the air, and the electricity generated by the fuel cells is supplied to a motor to produce driving force. Such fuel cell electric vehicles are also provided with hydrogen tanks which are easier managed than liquid hydrogen. Hydrogen vehicles have been another focus of attention from an environmental viewpoint, as automobiles that have combustion engines but use hydrogen as fuel instead of gasoline, and such hydrogen vehicles are also provided with hydrogen tanks for the same reason.
The hydrogen tanks used in fuel cell electric vehicles and hydrogen vehicles are high-pressure hydrogen storage containers with barrel-shaped exteriors, which consist of a metal or resin inner layer (liner) that directly contacts with the hydrogen gas, and a fiber-reinforced resin layer laminated on the outer surface (see Japanese Unexamined Patent Publication (Kokai) Nos. 2002-188794 and 2004-176898)
However, when a metal such as aluminum is used as the hydrogen tank liner, it exhibits excellent gas barrier properties but also absorbs hydrogen, leading to brittle fracture at low temperatures. When high-density polyethylene is used, sealability is exhibited for relatively high molecular weight natural gas but the gas barrier property for low molecular weight hydrogen is poor.
The use of polyamide resins that have more excellent gas barrier properties than high-density polyethylene has been proposed for hydrogen tank liner materials.
Incidentally, hydrogen tank liner materials must have high impact resistance because strong impact during use of hydrogen tank liners can cause cracking and lead to gas leakage, and improved impact resistance has been achieved by adding impact-resistant materials to polyamide resins.
However, when the internal pressure of a hydrogen tank is set to a high pressure of 70 MPa with an aim toward lengthening travel distance, the hydrogen tank must be at quite a low temperature during high-speed travel, and hence excellent impact resistance must be exhibited even at cryogenic temperatures of −40° C. and below.
It is an object of the present invention to solve the aforementioned problems by providing a hydrogen tank liner material with excellent gas barrier properties and with excellent impact resistance even at cryogenic temperatures of −40° C. and below, as well as to a hydrogen tank liner produced using it.